The invention relates to improvements in calenders and analogous machines for treating running webs of paper, textile material and the like. More particularly, the invention relates to improvements in guards for the inlet sides of nips of the rolls in such machines. Still more particularly, the invention relates to improvements in guards of the type wherein a support which extends longitudinally of the nip of two rolls carries two strip-shaped blocking devices (hereinafter called strips for short) each of which is adjacent one of the rolls and which flank the inlet side of the nip to thus protect the limbs of operators by preventing them from being drawn into the nip.
Commonly owned German Utility Model No. 70 00 740 discloses a guard wherein the support is assembled of several sheet metal profiles and portions of the profiles constitute two elongated strips each adjacent one of the rolls which form the nip. The interior of the support is filled with a foamed hard synthetic plastic material which serves to reduce the likelihood of vibration of the support and of the strips. Each strip is rigid with the support and is deformed with the latter, especially in the middle if the support forms part of a guard for a long nip. The length of a nip can be in the range of up to 10 meters.
A drawback of such guards is that it is very difficult or impossible to maintain each and every portion of each strip at a predeterminied distance from the peripheral surface of the respective roll. The width of clearances between the strips and the rolls is prescribed by the authorities and by the manufacturers. In many countries, the width of clearances between the strips and the respective rolls cannot exceed 8 mm. Adherence to such regulations would present no problems if the deformation of the support for the strips would invariably conform to the deformation of the adjacent rolls. However, the weight of the support causes it to bend, especially midway between its ends, and such bending is independent of and does not match the bending of the rolls which define the nip adjacent the guard. Additional reasons for departure of the width of clearances between the strips and the respective rolls from the prescribed width involve unavoidable manufacturing tolerances, especially as concerns the profiles of the support, as well as distortions of the rolls and/or of the guard as a result of heating or cooling.
Commonly owned German Utility Model No. 1 987 469 discloses a guard which is used in conjunction with takeup reels for webs of paper or other sheet materials. A single elongated strip of the guard is mounted on or forms part of a pivotable lever. The latter can turn about the axis of a guide roll which directs the web against the periphery of the growing supply of convoluted material on the core of the takeup reel. The guard further comprises means for maintaining the strip at a substantially constant distance from the exterior of the growing roll of convoluted sheet material on the takeup reel. The strip is rigid so that each and every portion thereof shares each and every movement of all other portions. The guard which is disclosed in this Utility Model exhibits the same drawbacks as the previously discussed guard, namely it cannot conform with a required degree of accuracy to the adjacent rotary component or components so that the width of the gap between the single strip and the adjacent rotating body is likely to vary with the axial direction of the rotating body. Such an arrangement would be unacceptable as a guard at the inlet side of the nip of a pair of relatively long and heavy rolls in a calender or a like machine.